1. Field of the Invention
The present invention relates to an instrument and method for measuring total luminous flux, which is one of the optical properties of luminous elements, and more particularly, to an instrument and method for measuring total luminous flux of luminous elements, which forms an approximately uniform spatial intensity distribution by simultaneously lighting a plurality of luminous elements for measurement in an integrating sphere when comparing a total luminous flux standard lamp with the luminous elements to measure the total luminous flux of the luminous elements, thus not requiring spatial mismatch error correction.
2. Description of Related Art
In general, a luminescent diode called a light emitting diode (LED) is a typical luminous element that converts electricity into light, in which minority carriers (electrons or holes) injected by means of a p-n junction structure of a semiconductor are produced and light is emitted by recombination of the carriers.
The performance of the LED can be evaluated with respect to energy efficiency, and the most important index for the evaluation is luminous efficacy. The luminous efficacy refers to the total luminous flux (unit: Im), which is the sum of light intensities emitted in all directions per electrical power input (unit: W), and is measured in units of Im/W.
Methods of measuring the total luminous flux that represents the optical properties of the luminous elements include an absolute measuring method using a goniophotometer and a relative measuring method using an integrating sphere and a total luminous flux standard lamp to measure the total luminous flux. Among them, an integrating sphere system applying the latter is widely used in the industrial field, since it is quick and easy to measure the total luminous flux and it is simple to ensure traceability using the standard lamp.
One of the major errors, which may occur in the total luminous flux measurement method using the integrating sphere, is spatial mismatch error, which occur due to a difference in the spatial intensity distribution (spatial intensity distribution) of light emitted from the total luminous flux standard lamp and the lamp for measurement. This error occurs because the internal structure of the integrating sphere used such as a baffle, a lamp holder, etc. and its limited reflectance of less than 100% cannot satisfy the conditions of an ideal integrating sphere with uniform spatial response, which makes it technically difficult to solve that error. Therefore, it is necessary to perform spatial mismatch correction by measuring a spatial response distribution function (SRDF) of the integrating sphere system for the total luminous flux measurement, measuring the spatial intensity distribution of the lamp for measurement, and calculating the measured results.
However, the relative measuring method using the integrating sphere requires a more complicated process to accurately perform the spatial mismatch correction than the absolute measuring method using the goniophotometer. Therefore, the integrating sphere system used in the industrial field, which is not aimed at maintaining the primary standard, generally employs the standard lamp having the same spatial intensity distribution as the lamp for measurement, thus reducing the spatial mismatch errors.
However, the spatial mismatch errors of the integrating sphere system become significant when measuring the total luminous flux of LEDs. The reason for this is that most LEDs are light sources having a certain directionality and also has different spatial intensity distributions from each other and thus it is difficult to apply a total luminous flux standard lamp suitable for each of the LEDs. Moreover, even if there is a suitable standard lamp, it requires much time and effort to match the spatial directions of the standard lamp and the lamp for measurement, thus deteriorating the efficiency of the measurement.